AVS 47th International Symposium
    Magnetic Interfaces and Nanostructures Friday Sessions
       Session MI-FrM

Invited Paper MI-FrM7
Femtosecond Spin Dynamics in Ferromagnetic Layered Systems

Friday, October 6, 2000, 10:20 am, Room 206

Session: Magnetic Recording: Media and Heads
Presenter: B. Koopmans, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
Ultrafast spin dynamics in ferromagnetic metals is an issue of great current interest. Pump-and-probe pulsed laser techniques have been successfully applied to study magnetism down to femtosecond time scales. Several groups have reported on an almost instantaneous (< 100 femtosecond) loss of magneto-optical contrast in nickel and cobalt films after excitation by a short laser pulse.@footnote 1@ These observations have triggered fundamental discussions as to the ultimate magnetic time scales, and the responsible scattering processes. In this presentation an introduction to time-resolved magneto-optical techniques and an overview of the rapidly developing field will be presented. In particular, it will be shown that ultimate care has to been taken in the interpretation of these experiments. Using a novel configuration we were able to demonstrate that during the first hundreds of femtoseconds a direct relation between magneto-optics and magnetism in ferromagnetic nickel does not exist. Nevertheless, using the distinct temperature dependence of the true demagnetization and that of optical artifacts, such as state-filling effects, we have been able to access the genuine magnetization dynamics. In our experiments on epitaxially grown Cu/Ni/Cu wedges evidence was found that the equilibration of the electron and spin systems takes place within approximately 0.5-1 picosecond. Oscillations on a much slower time scale, hundreds of picoseconds, were interpreted as a precession of the magnetization vector, triggered by the optical heating pulse. The latter phenomenon may be applied as all-optical real-time ferromagnetic resonance for the investigation of magnetic devices with a sub-micrometer spatial resolution. . @FootnoteText@ @footnote 1@ See e.g. E. Beaurepaire et al., Phys. Rev. Lett. 76, 4250 (1996); J. Hohlfeld et al., Phys. Rev. Lett. 78, 4861 (1997); J. Gadde et al., Phys. Rev. B 59, R6608 (1999).